Electromagnetic wave permeable window



- June 6, 1967 H. M. wzlss ELECTROMAGNETIC WAVE PERMEABLE WINDOW FiledMay 6, 1964 2 Sheets-Sheet 1 I as INVENT OR. HARRY MAX WEISS BY WW8;

June 6, 1967 H. M. WEISS 3,324,427

ELECTROMAGNETIC WAVE PERMEABLE WINDOW Filed May'6, 1964 2 Sheets-Sheet 2INVENTOR. jg. 7 HARRY MAX WEISS BY Mffififi United States Patent3,324,427 ELECTROMAGNETIC WAVE PERMEABLE WKNDUW Harry Max Weiss, SanJose, Caiifi, assignor, by mesne assignments, to Varian Associates, acorporation of California Filed May 6, 1964, Ser. No. 365,253 7 Claims.(Cl. 333-98) This invention relates to electromagnetic wave permeablewindows and more particularly to gas tight electromagnetic wavepermeable windows that may be utilized at the input or output of asource of electromagnetic wave energy, such as a microwave tube, tohermetically isolate the evacuated portion of the wave source.

Heretofore in the prior art, wave permeable windows have been insertedwithin hollow electromagnetic wave transmission devices, such aswaveguides, to provide gas tight partitions thereacross. Such windowsare fabricated from a suitable dielectric material, such as mica,ceramic, quartz or the like, and have their circumferential end portionshermetically secured to the inner walls of the waveguide. Such windowsmay be located within the waveguide to form a perpendicular transversewall, a slanted wall, a conical wall, etc. Preferred use of some ofthese windows require that they be placed within the waveguide at anarea containing strong electric fields. These electric fields, if ofsufficient magnitude, cause arcing at the seal area, that is, where thecircumferential edges of the window are hermetically sealed to the innerperipheral surface of the waveguide, thereby limiting the amount ofelectromagnetic power that can be passed through the window. The arcingalso causes puncturing of the dielectric window assembly resulting inloss of the vacuum and destruction of the tube. Also, thecircumferential edges of prior art windows and the inner peripheralsurfaces of the waveguides to which they are sealed must be veryaccurately controlled to produce satisfactory hermetic seals whichcauses such prior art window assemblies to be relatively diflicult andexpensive to fabricate.

Accordingly, an object of this invention is to overcome these and otherdisadvantages of the prior art.

Another object of this invention is to provide an improved wavepermeable window assembly.

Another object of this invention is to provide a wave permeable windowthat is readily sealed to waveguide means.

Still another object of this invention is to provide a gas tight, wavepermeable window capable of passing large amounts of electromagneticenergy therethrough.

A further object of this invention is to provide a gas tight, wavepermeable window assembly capable of passing therethroughelectromagnetic energy greatly in excess of several megawatts peak powerwithout producing arc- These and other objects of the present inventionare accomplished by a gas tight, electromagnetic wave permeable windowwhich includes a single or unitary wave permeable, gas tight, body whichis adapted to provide a path for electromagnetic energy therethrough.The unitary wave permeable body has an electromagnetic wave confiningportion with an electrically conductive coating on the exterior surfacethereof for providing a current path for electromagnetic energy and awindow portion disposed within the wave confining portion to provide agas tight portion across the wave confining portion. The window portionmay be located transversely across the wave confining portion and mayhave a thickness substantially less than one-half an electricalwavelength of the center frequency of the passband of the wave confiningportion whereas the wave confining portion may Too have a length of n/ 2electrical wavelengths where n can be any odd integer value.

These and other objects, features and advantages of the presentinvention will be readily apparent from consideration of the followingdetailed description taken in conjunction with the annexed drawingswherein:

FIGURE 1 illustrates in partial cross-section one embodiment of thepresent invention used in conjunction with a microwave tube, such as aklystron;

FIGURE 2A illustrates a section taken along the line 2A2A of FIGURE 1;

FIGURE 2B illustrates a modification of the device shown in FIGURE 2A;and

FIGURES 3, 4, 5, 6 and 7 illustrate various embodiments of the presentinvention.

Referring now to the drawings, there is illustrated in FIGURE 1 amicrowave tube, such as a klystron, which includes a gun section 11 forproducing an electron beam, a radio frequency interaction section 12 anda collector section 13. As is well known to those skilled in the art,the electron gun section, the interaction section and the collectorsection are united in axial alignment to enable the projection of theelectron beam produced by the gun section 11 through a series of drifttube sections 14. Each drift tube section terminates within a cavity 15,16 or 17 and has a conically tapered end portion 18 spaced from the endof an associated drift tube section to provide an interaction gap 19therebetween. The drift tube sections are supported in axially spacedalignment by relatively heavy transversely extending annular metallicplates 20 which form end portions of-the cavities 15, 16 and 17.

The cavity 17, adjacent the collector 13, illustrated in cross-sectionin FIGURE l-is an output cavity. High frequency electromagnetic energycontained within the output cavity is withdrawn therefrom by Way of afirst tubular waveguide 25, which may be rectangular. The end of thefirst waveguide remote from the output cavity is flanged 26 in a manneras illustrated in FIGURE 1.

A second tubular waveguide 31, which also may be a rectangularwaveguide, likewise has a flanged 32 end portion. The flanged portions26 and 32 of the first 25- and second 31 waveguides, respectively, arespaced apart but adjacent one another and the first and sec-0ndwaveguides have their longitudinal axis in substantial alignment.

Disposed between the flanged portions is a unitary or single, gas tight,electromagnetic wave permeable body 27. The wave permeable body includesa Wave confining portion, such as a flanged, tubular or hollowcylindrical portion 28. An electrically conductive coating or surface 29is secured to the exterior surface and edges of the electromagnetic waveconfining portion 28. Opposite ends of the wave confining portion 28 arehermetically sealed to the flanged portions 26 and 32, respectively,thereby electrically coupling the coating 29 to the first and secondwaveguides 25 and 31. The unitary wave permeable body 27 also includes awindow portion 30 which extends transversely of and is enclosed withinthe wave confining portion 28 to provide a gas tight, wave permeablepartition across the wave confining portion.

The single wave permeable member 27 and the flanged portions 26 and 32of the first and second waveguides 25 and 31, respectively, form acircular broadband waveguide wherein refiections from variousdiscontinuities and irregularities associated therewith cancel with outover a very broad band of frequency. In accordance with a preferredembodiment of the present invention, the tubular portion 28 of theunitary wave permeable body has a length parallel to the longitudinalaxis of the first 25 and second 31 waveguides of about 11/2 electricalwavelengths long at the center frequency of the passband of the tubularportion 28, where n can be any odd integer value. Although it may be anyodd integer value, a value of n equal to one produces a wider bandpassthan when n is greater than one. Also, the window portion of the wavepermeable member has a thickness substantially less than one-half of anelectrical Wevelength at the center frequency of the passhand of thetubular waveguide portion 28 and is substantially equally spaced fromopposite ends of the waveguiding portion 28. The broadband devicecomprising the wave permeable body 27 and the flanged portions 26 and 32of the first and second waveguides have a bandwidth that approaches 30%,that is, 30% between standing wave ratio points of 1.2.

The operation of the device illustrated in FIGURE 1 is such thatelectromagnetic energy contained Within the output cavity 17 passesthrough the first waveguide 25, the unitary wave permeable body 27 andthe second waveguide 31. Current paths associated with thiselectromagnetic energy is along the inner walls of the first waveguide25, the flanged portion 26 of the first waveguide 25, the electricallyconductive coating 29 on the unitary ceramic body 27, the flangedportion 32 of the second waveguide 31 and the inner peripheral walls ofthe second waveguride 31.

The broadband device, comprising the unitary ceramic body 27 and theflanged waveguide portions 26 and 32, operates such that a standing waveis created therein that has a maximum electric field intensity at anarea substantially equally spaced between the ends of the waveguidingportion 28 which field decreases to substantially zero intensity at theopposite ends of the waveguiding portion 28 adjacent the flangedportions 26 and 32. Accordingly, no arcing occurs where the flangedportions 26 and 32 are sealed to opposite ends of the waveguidingportion 28 of the wave permeable body 27 since substantially no electricfield is present at the seal area. Due to the unitary construction ofthe wave permeable body 27, there is no metallic sealing materialintermediate the ends of the waveguiding portion (for example, where thewindow portion 30 intercepts the waveguiding portion 28) at which arcingmay take place as is the case in prior art devices. An excess of 100megawatts of peak power in the S band has been transmitted through thedevice of FIGURE 1 without producing arcing, whereas with prior artwindows arcing occurs in the vicinity of twenty megawatts of peak powerin the S band. The arcing in prior art broadband devices is due to thefact that heretofore sealing material has been required at areas of highelectric field intensity in order to preserve the wide bandwidthcharacteristics. For example, the bandwidth of the tubular waveguidingportion 28 is largest when the window portion 30 is locatedsubstantially an equal distance between the ends of the waveguidingportion 28 where the electric field intensity is a maximum.

It is clear that the flanged portions 26 and 32 function as transitionmeans which electrically couple the conductive coating 29 on the unitarypermeable body to the first 25 and second 31 waveguides. Also, it isclear that the wave permeable body 27 being air tight and hermeticallysealed to at least the flanged portion 26 of the first waveguide servesto hermetically isolate the evacuated portion of the klystron. Asuitable dielectric material which is vacuum tight, such as mica,quartz, ceramic and the like, can be used to fabricate the unitary wavepermeable body 27.

The flanged portions 26 and 32 of the first 25 and second 31 waveguides,respectively, are readily hermetically secured to opposite ends of thewaveguiding portion 28 of the unitary body 27 by an ordinary butt sealin a manner as illustrated in FIGURE 1. As will be obvious to thoseskilled in the art, this type of seal eliminates the exact dimensioningof the circumferential edges of prior art windows and the innerperipheral surfaces of the waveguides to which they are sealed necessaryto fabricate prior art output window assemblies. Accord- 4 ingly, theoutput window assembly illustrated in FIGURE 1 is readily andeconomically fabricated.

The electrically conductive coating 29 on the exterior surface of thewaveguiding portion 28 of the wave permeable body may be evaporated,flame sprayed, metalized or otherwise suitably applied to the wavepermeable body. For example, FIGURE 2A, which is a section taken alongthe line 2A2A of FIGURE 1 shows a metalized layer 35 over the exteriorsurface of the tubular waveguiding portion 28 which is then plated witha layer of a low electrical resistance material 36, such as copper. Thewaveguiding portion 28 of the wave permeable body is not limited tobeing circular, as shown in FIGURE 2A, for it may take any desiredgeometric shape. For example, FIGURE 2B illustrates a single, wavepermeable body with a rectangular waveguiding portion 37 having anelectrically conductive surface 38 on the exterior surface thereof.

FIGURES 3 through 8 illustrate various modifications of the deviceillustrated in FIGURE 1. For example, FIG- URE 3 illustrates a unitarywave permeable member 39, substantially similar to the member 27 ofFIGURE 1, having a hollow passageway 40 extending through the windowportion whereby a gas or liquid may be readily passed through the windowportion to prevent the window from overheating as a result of absorbingelectromagnetic energy propagated therethrough. The gas or liquid entersand leaves the window area by any suitable means, such as an inlettubulation 41 and an outlet tubulation 42, respectively. A furthermodification of this device is illustrated in FIGURE 4 where the hollowpassageway within the window portion is greatly increased by using twoparallel window portions 45 and 46. This removes the window portionsfrom the area of maximum electrical field thereby decreasing thebandwidth of the device. However, this disadvantage is overcome by thelarge amounts of electromagnetic energy that may be passed through thedevice of FIGURE 4 without overheating the Window portions 45 and 46.

Another embodiment of the present invention is illustrated in FIGURE 5wherein there is shown a unitary wave permeable body 50 having a windowportion 51 which comprises a section of a hollow sphere. This type ofconstruction mechanically strengthens the window portion 51 and enablesit to withstand great pressure differentials existing on opposite sidesthereof. Also, electromagnetic energy traveling from left to rightthrough the device of FIGURE 5, from a vacuum source, will producesubstantially less multipactor at the window 51 than would a flattransverse window. A modification of this embodiment is illustrated inFIGURE 6 which shows a hollow window portion 52 which is adapted to becooled by passrng liquids or gases therethrough and in which each sideof the window portion 52 comprises a section of a hollow sphere. Thisembodiment permits multipactor reduction regardless of which side isconnected to the source of electromagentic energy and also provides astrong window assembly capable of withstanding differential pressures.

FIGURE 7 illustrates still another embodiment of the present inventionwherein a unitary, wave permeable body has a window portion 55 thatslants across a waveguiding or confining portion 56.

What has been described is an electromagnetic wave permeable windowincluding a single, gas tight, wave permeable body adapted to provide apath for electromagnetic energy therethrough. The wave permeable bodyincludes a wave confining portion having an electrically conductivecoating on the exterior surface thereof for providing a current path forelectromagnetic energy and also includes at least one window portionthat extends across the path of the electromagnetic energy and which isenclosed in the wave confining portion of the wave permeable body.

Since many changes could be made in the above embodiments, and sincemany apparent widely different embodiments of the present inventioncould be made without departing from the spirit and scope thereof, it isintended that all material contained in the above description or shownin the accompanying drawings shall be interpreted as illustrative onlyand not in a limiting sense.

What is claimed is:

1. An electromagnetic wave permeable window assembly for transmittingelectromagnetic energy comprising: a pair of waveguides having theirlongitudinal axis in substantial alignment, adjacent ends of saidwaveguides being flanged, a broadband device located between and securedto said flanged portions for providing a path for electromagnetic energybetween said pair of waveguides, said broadband device including aunitary ceramic body having a window portion extending across the pathof electromagnetic energy at a point of high electric field, saidceramic body also including a flanged portion around the circumferenceof said window portion which flanged portion is parallel to thelongitudinal axis of said pair of waveguides, and an electricallyconductive coating on the exterior surface of said wave permeable bodyflanged portion, said conductive coating being electrically coupled tosaid waveguides by way of hermetic seals between said ceramic body andsaid waveguide flanged portions at a distance from said window portionalong said longitudinal axis corresponding with points of reducedelectric field.

2. The window assembly according claim 1 wherein said window portionslants across the path of electromagnetic energy.

3. The window assembly according to claim 1 wherein said window portionis characterized as being a section of a hollow sphere.

4. A gas tight electromagnetic wave permeable window assembly fortransmitting electromagnetic energy therethrough comprising: first andsecond tubular waveguide members having adjacent end portions, windowmeans including a unitary wave permeable body having an electricallyconductive coating on the exterior surface thereof located between saidadjacent end portions of said first and second waveguide members, saidwave permeable body including a circumferential electromagneticwaveguiding portion having a length of n/2 electrical wave lengths atthe center frequency of the passband of said waveguiding portion where ncan be any odd integer value, said wave permeable body also including awindow portion disposed within said waveguiding portion to form a gastight wave permeable partition across said wave guiding portionsubstantially at the center thereof, and transition means includinghermetic seals connecting said first and second Waveguide members toopposite ends of said waveguiding portion of said Wave permeable bodywhereby said transition means are electrically coupled to saidconductive coating on the exterior of said waveguiding portion.

5. The combination according to claim 4 wherein n is equal to one.

6. A high frequency gas tight wave permeable window assembly fortransmitting electromagnetic energy comprising: first and second tubularwaveguide members having adjacent end portions, window means including aunitary wave permeable body located between said adjacent end portionsof said first and second waveguide members, said wave permeable bodyincluding a circumferential electromagnetic waveguiding portion havingan electrically conductive coating on the exterior surface thereof forproviding a current path for electromagnetic energy, said waveguidingportion having a length approximately n/ 2 electrical wavelengths longat the center frequency of the passband of said waveguiding portionwhere n can be any odd integer value, said wave permeable body alsoincluding a window portion disposed transversely of and within saidwaveguiding portion to form a gas tight wave permeable partition acrossthe waveguiding portion, said window portion disposed substantiallymidway the length of said waveguiding portion and having a thicknesssubstantially less than one-half an electrical wavelength at the centerfrequency of the passband of the wave con fining portion, and transitionmeans hermetically connecting said first and second waveguide members toopposite ends of said waveguiding portion of said wave permeable bodywhereby said transition means are electrically coupled to saidconductive coating on the exterior of said waveguiding portion of saidWave permeable body.

7. The combination according to claim 4 wherein said first and secondwaveguide members are rectangular and said waveguide portion of saidpermeable body is circular, the diameter of said circular waveguideportion being greater than the width of said first and secondwaveguides.

References Cited UNITED STATES PATENTS 2,683,863 7/1954 Curtis 333982,706,275 4/1955 Clark 33398 2,958,834 11/1960 Symons 33398 2,971,1722/1961 Hamilton 33398 2,990,526 6/ 1961 Shelton 33398 3,101,461 8/1963Henry-Bezy 33398 3,100,881 8/1963 Edson 33398 3,110,000 11/1963Churchill 33398 3,210,699 10/ 1965 Hisashi-Tagano 33398 FOREIGN PATENTS1,341,625 9/1963 France.

HERMAN KARL SAALBACH, Primary Examiner.

L. ALLAHUT, Examiner.

1. AN ELECTROMAGNETIC WAVE PERMEABLE WINDOW ASSEMBLY FOR TRANSMITTINGELECTROMAGNETIC ENERGY COMPRISING: A PAIR OF WAVEGUIDES HAVING THEIRLONGITUDINAL AXIS IN SUBSTANTIAL ALIGNMENT, ADJACENT ENDS OF SAIDWAVEGUIDES BEING FLANGED, A BROADBAND DEVICE LOCATED BETWEEN AND SECUREDTO SAID FLANGED PORTIONS FOR PROVIDING A PATH FOR ELECTROMAGNETIC ENERGYBETWEEN SAID PAIR OF WAVEGUIDES, SAID BROADBAND DEVICE INCLUDING AUNITARY CERAMIC BODY HAVING A WINDOW PORTION EXTENDING ACROSS THE PATHOF ELECTROMAGNETIC ENERGY AT A POINT OF HIGH ELECTRIC FIELD, SAIDCERAMIC BODY ALSO INCLUDING A FLANGED PORTION AROUND THE CIRCUMFERENCEOF SAID WINDOW PORTION WHICH FLANGED PORTION IS PARALLEL TO THELONGITUDINAL AXIS OF SAID PAIR OF WAVEGUIDES, AND AN ELECTRICALLYCONDUCTIVE COATING ON THE EXTERIOR SURFACE OF SAID WAVE PERMEABLE BODYFLANGED PORTION, SAID CONDUCTIVE COATING BEING ELECTRICALLY COUPLED TOSAID WAVEGUIDES BY WAY OF HERMETIC SEALS BETWEEN SAID CERAMIC BODY ANDSAID WAVEGUIDE FLANGED PORTIONS AT A DISTANCE FROM SAID WINDOW PORTIONALONG SAID LONGITUDINAL AXIS CORRESPONDING WITH POINTS OF REDUCEDELECTRIC FIELD.